Fig. 17 - Chart of Minimum Clearances for Blowers.
Moving the gears "OUT" or "IN" on the rotor shafts is
check the clearance between the LEADING edge of the
accomplished by adding or removing shims between the
UPPER and the TRAILING edge of the LOWER rotors
("C" clearance) for the minimum clearance shown in Fig.
The clearance between the rotor lobes should be
17. Rotor-to-rotor measurements should
checked with 1/2" wide feeler gages in the manner
from each end and at the center of the blower.
shown in Fig. 16. When measuring clearances of more
than .005", laminated feeler gages that are made up of
2. After determining the amount one rotor must be
.002", .003" or .005" feeler stock are more practical and
revolved to obtain the proper clearance, add shims back
suitable than a single feeler gage. Clearances should
of the proper gear to produce the desired result. When
be measured from both the inlet and outlet sides of the
more or less shims are required, both gears must be
removed from the rotors. Placing a .003" shim in back
A specially designed feeler gage set J 1698-02 for the
of a rotor gear will revolve the rotor .001 ".
blower clearance operation is available. Time the rotors
3. Install the required thickness of shims back of the
1. 71 Blower - Timing the rotors to have .002" or .004"
proper gear and next to the bearing inner race and
to .006" or .008" clearance between the TRAILING edge
reinstall both gears. Recheck the clearances between
the rotor lobes.
of the UPPER rotor and LEADING edge of the LOWER
rotor ("CC" clearance) measured from both the inlet and
keep this clearance to the minimum dimension. Then